I don't think your being selfish at all, it is your wedding, not hers. Her monetary contribution shouldn't change that. It sounds like your mom is living her wedding dreams through you. Did she not get to plan her own wedding?
I had to deal with this on a smaller scale with my mom too. Her wedding 35 years ago was at her parents house with 50 people, no dancing, and a store bought cake. When we first got engaged she got all crazy about over planning and booking all sorts
of things. She was going to start booking vendors without consulting me because she thought she was doing me a favor. More than once I had to gently remind her that this wasn't her wedding, and that we would have different tastes and opinions on
many things. It was frustrating because I felt like a total bridezilla whenever I talked to her.
What finally made things click in my mom's head was that we had drastically different opinions on the wedding cake topper. (kind of trivial, I know) She wanted us to use the cake topper from her wedding which is fragile blown glass with birds. It's
really beautiful, but I wanted something more fun, that reflected DH and myself. I know that it hurt her feelings, but she finally realized that our wedding needed to reflect us, not her. My dad had to step in and tell her that too, along
with my brothers. I think hearing it from someone other than me, really helped change her mind. The last few months of planning, she was awesome.
I don't know what advice to offer you except to try and get your family to help persuade your mom that no matter who's paying, it's your and your FI's wedding, not hers. And that you are eternally grateful for her love and support, but that
she needs to back off a bit.
Sorry this ended up so long. Good luck!